1. Field of the Invention
This invention relates to apparatus for the hypodermic injection of fluids.
2. Description of the Prior Art
Hypodermic fluid dispensers fall into two broad categories, namely, needle hypodermic dispensers and needle-less injectors, such as jet injectors. In the past, jet injectors have been particularly useful in large scale immunization programs, such as those administered by the World Health Organization (WHO) or the military, for example, where the number of subjects to be immunized in a single session is very large (more than 200 injections per session). However, in recent years, jet injectors are also finding benefit in more routine immunizations at WHO health centers around the world, where the number of subjects injected is relatively small at less than 40 injections per session.
In general, jet inoculation, as compared to needle inoculation, is less traumatic, requires less operator training, and allows a higher number of procedures per unit of time.
Although both needle hypodermic injectors and high pressure jet injectors have been widely used, the presently known devices have serious disadvantages with respect to the injection of humans and animals alike. There exists a high level of belief that conventional jet injectors are capable of cross-infection when the same orifice is used for subsequent injections, and the problems associated with needle injectors in the spread of AIDS (Acquired Immune Deficiency Syndrome) alone is sufficient motivation to avoid proliferation of today's needle systems. People cannot be relied upon to dispose of needle injectors in accordance with instructions and good practice, and an element of the population are tempted to reuse needles without knowledge of or regard for safe practices.
There are other important shortcomings in the present state of the art with respect to the inoculation of humans and large animals, such as cattle and pigs. In the case of large animals, needles used for injecting vaccines, vitamins, medications and hormones in large, food-producing animals often cause damage to prime portions of the meat through the creation of abscesses and scars, resulting in serious economic loss to the industry. In the majority of cases, these factors are even more prevalent because the needle injectors become dull or bent when used for multiple injections, which is a common practice in the industry. In addition, due to increased awareness of cross-infection in food-producing animals, agricultural leaders recommend that needles no longer be reused for animal injections. Furthermore, it is not at all unusual for multiple injections to be scheduled within the same period of time, this being true for humans and animals as well. However, repeated injections are usually met with greater resistance by the recipient and also makes the procedure far more expensive. Hence, other important shortcomings would be overcome if more than one material could be injected at the same time.
Properly configured jet injectors provide the best chance for reducing the problems of cross-contamination, as well as the case where more than one injection is required at the same time, and could reduce the time to train people involved in the injection process. If jet injectors were effective for both animals and humans, a higher number of procedures per unit of time would be possible. The higher number of procedures is particularly important in the beef and dairy industry where each day a certain number of animals receive injections. This is also true for the multiple vaccine requirement for children.
Large animal hide, such as cowhide, can be very thick, often in the range of 1/8 inch to 3/8 inch or more in thickness. The hide includes the hair, a tough outer layer, and thereafter the dermis, whose inside surface has a rubber-like interface that begins the subcutaneous ("sub-Q") layer that separates the hide and the muscle. In cattle, injections are usually given in the neck, a leg or a hind quarter. A known CO.sub.2 -driven jet injector was experimentally tested on a freshly euthanized cow and the injection site was immediately followed by a pathologist's examination. It was found that the injection rarely penetrated the desired depth into the muscle.
Electrically operated needle-less injectors, previously disclosed, often require batteries, since standard power sources are not available at remote or isolated areas where injections are often given. People responsible for the immunization programs at these locations are concerned about disposal of these batteries, leading to the recommendation that rechargeable batteries be used. Indeed, the use of any electrically-powered injector used away from standard power sources would be enhanced if there were no batteries to be disposed of, yet sufficient electrical power were available.
The exit path of needle-less injectors, referred to as "orifices," present additional problems. Orifices are commonly found in the range of 0.004 to 0.014 inches. Extensive experimentation has shown that these orifices are likely to be ineffective for deep injections unless virtually perfect in structure and optimized in diameter for that particular injection site. If the orifices are poorly configured, they will fail to penetrate the thick hide of an animal, and satisfactory deep injections will not occur no matter what pressure is applied on the serum or other product being injected. When poorly configured orifices with diameters in tile range of 0.004 to 0.014 inches are used with injection pressures as high as 2,000 to 10,000 psi, effective deep injections have not been possible.
It is important that the speed at which needle-less injections are made is high, whereby the entire dose, or doses, enters the animal's body quickly by way of the high velocity jet stream. Movement could cause a loss of the initial penetration point and the injection could fail. As noted above with respect to cows, the injection must clear a hide thickness of 3/8 inch, or more in some cases, to achieve intramuscular ("IM") injection. Speed of injection, orifice size, quality of the jet stream, and lack of movement are necessary to get good IM injection results. If any of these characteristics are not fully met, or if the jet stream breaks down when the injection material is designed for an IM injection, the fluid will remain in the dermis, or in the subcutaneous layer instead, and could result in a less-effective or even a totally useless injection.
Presently known collapsible bodies or containers (generally referred to hereinafter as "containers") for holding hypodermic fluid do not readily provide the necessary fluid even when sufficient pressure is applied to the collapsible container. Collapsible containers do not exist for effecting the proper mixing of ingredients at the time sufficient pressure is applied to the collapsible container.
Present needle-less jet injector systems are very expensive. For one thing, these systems draw the serum or other injecting fluid into disposable capsules having walls thick enough to withstand the high pressures of about 1,700 psi or more for human IM injections.
Another problem with jet injector systems is that they "gum up" from the injectant material if the user fails to thoroughly clean the device on a timely basis. In some situations, such as field use with cattle, this procedure is difficult, if not impossible, in terms of available time and equipment.
Some injection fluids have higher viscosities than water, such as the BST growth hormone, Posilac, for enhancing milk production. If the fluid becomes too viscous because of lower temperatures, proper injection would not be possible. Presently, no temperature measuring systems for injection fluids are available.